U.S. patent number 8,720,257 [Application Number 12/987,340] was granted by the patent office on 2014-05-13 for methods, systems and apparatus for detecting material defects in combustors of combustion turbine engines.
This patent grant is currently assigned to General Electric Company. The grantee listed for this patent is Saurav Dugar, Dullal Ghosh, Gilbert Otto Kraemer, Anthony Wayne Krull, Tejas Bharat Shinde. Invention is credited to Saurav Dugar, Dullal Ghosh, Gilbert Otto Kraemer, Anthony Wayne Krull, Tejas Bharat Shinde.
United States Patent |
8,720,257 |
Krull , et al. |
May 13, 2014 |
Methods, systems and apparatus for detecting material defects in
combustors of combustion turbine engines
Abstract
A method for detecting defects in a combustion duct in a
combustion system of a turbine engine while the turbine engine
operates, wherein the combustion duct comprises an inner surface,
which, during operation, is exposed to the hot-gas flowpath, the
method comprising the steps of: providing a first electrode that is
electrically connected to the combustion duct; providing a second
electrode that resides within the hot-gas flowpath; applying a
voltage across the first electrode and the second electrode; and
detecting current flowing between the first electrode and the
second electrode.
Inventors: |
Krull; Anthony Wayne (Anderson,
SC), Ghosh; Dullal (Orissa, IN), Dugar; Saurav
(West Bengal, IN), Shinde; Tejas Bharat (Maharashtra,
IN), Kraemer; Gilbert Otto (Greer, SC) |
Applicant: |
Name |
City |
State |
Country |
Type |
Krull; Anthony Wayne
Ghosh; Dullal
Dugar; Saurav
Shinde; Tejas Bharat
Kraemer; Gilbert Otto |
Anderson
Orissa
West Bengal
Maharashtra
Greer |
SC
N/A
N/A
N/A
SC |
US
IN
IN
IN
US |
|
|
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
46330811 |
Appl.
No.: |
12/987,340 |
Filed: |
January 10, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120176248 A1 |
Jul 12, 2012 |
|
Current U.S.
Class: |
73/112.01 |
Current CPC
Class: |
G01N
27/20 (20130101); F02C 7/30 (20130101); G01M
15/14 (20130101); F05D 2260/80 (20130101); Y02T
50/60 (20130101) |
Current International
Class: |
G01M
15/14 (20060101) |
Field of
Search: |
;73/112.01,112.03,112.05,118.03 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Search Report and Written Opinion from FR Application No. 1250251
dated Jun. 4, 2013. cited by applicant.
|
Primary Examiner: McCall; Eric S
Attorney, Agent or Firm: Henderson; Mark E. Cusick; Ernest
G. Landgraff; Frank A.
Claims
We claim:
1. A system for detecting defects in a combustion duct of a
combustion system of a combustion turbine engine while the
combustion turbine engine operates, wherein, the combustion duct
comprises an inner surface, which, during operation, is exposed to
the combustion gases of the hot-gas flowpath, the system
comprising: an insulator coating disposed on the inner surface of
the combustion duct; a first electrode that is electrically
connected to the combustion duct; a second electrode that resides
within the hot-gas flowpath; means for inducing a voltage across
the first electrode and the second electrode; and means for
detecting current flowing between the first electrode and the
second electrode; wherein the second electrode extends through the
combustion duct and comprises insulating structure that insulates
the second electrode from being electrically connected to the
combustion duct; wherein the second electrode comprises a
conducting tip at a distal end that projects into the hot-gas
flowpath through the combustion duct; wherein the second electrode
comprises a position that is downstream of at least a majority of
the combustion duct to which the first electrode is electrically
connected; wherein the insulator coating comprises a thermal
barrier coating; and wherein the combustion duct comprises one of a
transition piece and a liner.
2. The system according to claim 1, wherein the second electrode
comprises a position that is in proximity to a downstream end of
the combustion duct to which the first electrode is electrically
connected; wherein the second electrode, during operation, is
electrically connected to the combustion gases flowing through the
combustion duct during operation of the combustion turbine
engine.
3. The system according to claim 1, wherein, during operation, the
hot-gas flowpath of the combustion turbine engine comprises an
electrically conductive doping agent; wherein the electrically
conductive doping agent is injected into the hot-gas flowpath at
predetermined testing intervals; and wherein the electrically
conductive doping agent is injected into the hot-gas flowpath at a
position that is upstream of the combustion duct.
4. The system according to claim 1, further comprising a control
unit; wherein the control unit comprises a voltage source that is
configured to apply a predetermined level of voltage across the
first electrode and the second electrode; and wherein the control
unit comprises an amp meter that is configured to detect current
flowing between the first electrode and the second electrode.
5. The system according to claim 4, wherein the control unit
comprises an amp meter that is configured to detect a level of
current flowing between the first electrode and the second
electrode; and wherein the control unit is configured to determine
whether the detected current level between the first electrode and
the second electrode exceeds a threshold current level.
6. The system according to claim 5, wherein the first electrode,
the second electrode, and the control unit are configured such that
when the insulator coating comprises a desired level of coverage
over the inner surface of the combustion duct, the predetermined
voltage level applied across the first electrode and the second
electrode fails to induce the detected current level between the
first electrode and the second electrode to exceed the threshold
current level.
7. The system according to claim 5, wherein the first electrode,
the second electrode, and the control unit are configured such
that: during a first operating condition, the detected current
level between the first electrode and the second electrode does not
exceed the threshold current level; and during a second operating
condition, the detected current level between the first electrode
and the second electrode exceeds the threshold current level;
wherein the second operating condition comprises an operating
conditioning in which a defect is present in the insulator
coating.
8. The system according to claim 7, wherein the defect comprises an
exposed area of a predetermined size on the inner surface of the
combustion duct, the exposed area comprising an area that is
substantially no longer covered by the insulator coating; and
wherein the predetermined size of the exposed area corresponds to
an area of exposure at which the predetermined voltage level
induces the detected current level to exceed the threshold current
level.
9. The system according to claim 7, wherein the defect comprises
one of spallation of the insulator coating and crack formation
within the inner surface of the combustion duct.
10. The system according to claim 7, wherein the first operating
condition comprises an operating condition in which a desired
portion of the inner surface of the combustion duct is covered by
the insulator coating; and wherein the control unit is configured
to issue a warning notification when the second operating condition
occurs.
11. The system according to claim 10, wherein: the insulator
coating comprises an electrical conductivity that is less than the
electrical conductivity of the combustion duct; the insulator
coating comprises an electrical conductivity that is less than the
approximate electrical conductivity of the combustion gases flowing
through the combustion duct during operation of the combustion
turbine engine; and the desired portion comprises substantially all
of the inner surface of the combustion duct.
12. A method for detecting defects in a combustion duct of a
combustion system of a combustion turbine engine while the
combustion turbine engine operates, wherein the combustion duct
comprises an inner surface, which, during operation, is exposed to
the combustion gases of the hot-gas flowpath, the method comprising
the steps of: providing a first electrode that is electrically
connected to the combustion duct; providing a second electrode that
resides within the hot-gas flowpath and within or in proximity to
the combustion duct; applying a voltage across the first electrode
and the second electrode; and detecting current flowing between the
first electrode and the second electrode; wherein the second
electrode comprises a conducting tip at a distal end that projects
into the hot-gas flowpath through the combustion duct; wherein the
second electrode comprises a position that is in proximity to a
downstream end of the combustion duct to which the first electrode
is electrically connected; wherein the insulator coating comprises
a thermal barrier coating; and wherein the combustion duct
comprises one of a transition piece and a liner.
13. The method according to claim 12, further comprising the step
of coating the inner surface of the combustion duct with an
insulator coating; wherein: the insulator coating comprises an
electrical conductivity that is less than the electrical
conductivity of the combustion duct; and the insulator coating
comprises an electrical conductivity that is less than the
approximate electrical conductivity of the combustion gases flowing
through the combustion duct during operation of the combustion
turbine engine.
14. The method according to claim 13, further comprising the steps
of: detecting a level of current flowing between the first
electrode and the second electrode; and determining whether the
detected current level exceeds a threshold current level.
15. The method according to claim 14, wherein the threshold current
level corresponds to a threshold above which detected current
levels comprise a high probability of being caused by a defect in
the insulator coating.
16. The method according to claim 15, wherein the defect comprises
an exposed area of predetermined size on the inner surface of the
combustion duct, the exposed area comprising an area that is
substantially no longer covered by the insulator coating; and
wherein the predetermined size of the exposed area corresponds to a
size at which the predetermined voltage level induces the detected
current level to exceed the threshold current level.
17. The method according to claim 15, wherein detected current
levels that do not exceed the threshold current level correspond to
current levels that occur when a desired portion of the inner
surface of the combustion duct remains covered by the insulator
coating; further comprising the step of issuing a warning
notification when the detected current level exceeds the threshold
current level.
18. The method according to claim 12, further comprising the step
of injecting an electrically conductive doping agent into the
hot-gas flowpath at a position that is upstream from the combustion
duct.
19. The method according the claim 18, wherein the electrically
conductive doping agent is configured to increase the electrical
conductivity of the combustion gases flowing through the hot-gas
flowpath during operation of the combustion turbine engine.
20. The method according to claim 19, wherein the electrically
conductive doping agent is injected periodically, the periods of
injection corresponding to a desired testing schedule.
Description
BACKGROUND OF THE INVENTION
This present application relates generally to methods, systems, and
apparatus for detecting defects, including surface defects, which
may occur in industrial manufacturing processes, engines, or
similar systems. More specifically, but not by way of limitation,
the present application relates to methods, systems, and apparatus
pertaining to the detection of defects that form on the components,
such as those found within the combustor, exposed to the hot-gases
of combustion turbine engines.
In operation, generally, a combustion turbine engine may combust a
fuel with compressed air supplied by a compressor. As used herein
and unless specifically stated otherwise, a combustion turbine
engine is meant to include all types of turbine or rotary
combustion engines, including gas turbine engines, aircraft
engines, etc. The resulting flow of hot gases, which typically is
referred to as the working fluid, is expanded through the turbine
section of the engine. The interaction of the working fluid with
the rotor blades of the turbine section induces rotation in the
turbine shaft. In this manner, the energy contained in the fuel is
converted into the mechanical energy of the rotating shaft, which,
for example, then may be used to rotate the rotor blades of the
compressor, such that the supply of compressed air needed for
combustion is produced, and the coils of a generator, such that
electrical power is generated. During operation, it will be
appreciated that components exposed to the hot-gas path become
highly stressed with extreme mechanical and thermal loads. This is
due to the extreme temperatures and velocity of the working fluid,
as well as the rotational velocity of the turbine. As higher firing
temperatures correspond to more efficient heat engines, technology
is ever pushing the limits of the materials used in these
applications.
Whether due to extreme temperature, mechanical loading or
combination of both, component failure remains a significant
concern in combustion turbine engines. A majority of failures can
be traced to material fatigue, which typically is forewarned by the
onset of crack propagation. More specifically, the formation of
cracks caused by material fatigue remains a primary indicator that
a component has reached the limit of its useful life and may be
nearing failure. The ability to detect the formation of cracks
remains an important industry objective, particularly when
considering the catastrophic damage that the failure of a single
component may occasion. Such a failure event may cause a chain
reaction that destroys downstream systems and components, which
require expensive repairs and lengthy forced outages.
One manner in which the useful life of hot-gas path components may
be extended is through the use of protective coatings, such as
thermal barrier coatings. In general, exposed surfaces are covered
with these coatings, and the coatings insulate the component
against the most extreme temperatures of the hot-gas path. However,
as one of ordinary skill in the art will appreciate, these types of
coatings wear or fragment during usage, a process that is typically
referred to as "coating spallation" or "spallation". Spallation may
result in the formation and growth of uncoated or exposed areas at
discrete areas or patches on the surface of the affected component.
These unprotected areas experience higher temperatures and, thus,
are subject to more rapid deterioration, including the premature
formation of fatigue cracks and other defects. In combustion
turbine engines, coating spallation is a particular concern for
turbine rotor blades and components within the combustor, such as
the transition piece. Early detection of coating spallation may
allow an operator to take corrective action before the component
becomes completely damaged from the increased thermal strain.
While the operators of combustion turbine engines want to avoid
using worn-out or compromised components that risk failing during
operation, they also have a competing interests of not prematurely
replacing components before their useful life is exhausted. That
is, operators want to exhaust the useful life of each component,
thereby minimizing part costs while also reducing the frequency of
engine outages for part replacements to occur. Accordingly,
accurate crack detection and/or coating spallation in engine
components is a significant industry need. However, conventional
methods generally require regular visual inspection of parts. While
useful, visual inspection is both time-consuming and requires the
engine be shutdown for a prolonged period.
The ability to monitor components in the hot-gas path while the
engine operates for the formation of cracks and the spallation of
protective coatings remains a longstanding need. What is needed is
a system by which crack formation and spallation may be monitored
while the engine operates so that necessary action may be taken
before a failure event occurs or significant component damage is
realized. Such a system also may extend the life of components as
the need for part replacement may be based on actual, measured wear
instead of what is anticipated. In addition, such a system would
decrease the need or frequency of performing evaluations, such as
visual inspections, that require engine shutdown. To the extent
that these objectives may be achieved in a cost-effective manner,
efficiency would be enhanced and industry demand would be high.
BRIEF DESCRIPTION OF THE INVENTION
The present invention, thus, describes system for detecting defects
in a combustion duct of a combustion system of a combustion turbine
engine while the combustion turbine engine operates, wherein, the
combustion duct comprises an inner surface, which, during
operation, is exposed to the combustion gases of the hot-gas
flowpath. In one embodiment, the system includes: an insulator
coating disposed on the inner surface of the combustion duct; a
first electrode that is electrically connected to the combustion
duct; a second electrode that resides within the hot-gas flowpath;
means for inducing a voltage across the first electrode and the
second electrode; and means for detecting current flowing between
the first electrode and the second electrode.
The present invention further describes a method for detecting
defects in a combustion duct of a combustion system of a combustion
turbine engine while the combustion turbine engine operates,
wherein the combustion duct comprises an inner surface, which,
during operation, is exposed to the combustion gases of the hot-gas
flowpath. In one embodiment, the method includes the steps of:
providing a first electrode that is electrically connected to the
combustion duct; providing a second electrode that resides within
the hot-gas flowpath and within or in proximity to the combustion
duct; applying a voltage across the first electrode and the second
electrode; and detecting current flowing between the first
electrode and the second electrode.
These and other features of the present application will become
apparent upon review of the following detailed description of the
preferred embodiments when taken in conjunction with the drawings
and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of this invention will be more completely
understood and appreciated by careful study of the following more
detailed description of exemplary embodiments of the invention
taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic representation of an exemplary turbine engine
in which embodiments of the present application may be used;
FIG. 2 is a sectional view of an exemplary compressor that may be
used in the gas turbine engine of FIG. 1;
FIG. 3 is a sectional view of an exemplary turbine that may be used
in the gas turbine engine of FIG. 1;
FIG. 4 is a sectional view of an exemplary combustor that may be
used in the gas turbine engine of FIG. 1 and in which the present
invention may be employed;
FIG. 5 is a perspective cutaway of an exemplary combustor in which
embodiments of the present invention may be employed; and
FIG. 6 illustrates cross-sectional view of a transition piece and a
system for monitoring material defects according to an exemplary
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the figures, FIG. 1 illustrates a schematic
representation of a gas turbine engine 100 in which embodiments of
the present invention may be employed. In general, gas turbine
engines operate by extracting energy from a pressurized flow of hot
gas that is produced by the combustion of a fuel in a stream of
compressed air. As illustrated in FIG. 1, gas turbine engine 100
may be configured with an axial compressor 106 that is mechanically
coupled by a common shaft or rotor to a downstream turbine section
or turbine 110, and a combustion system 112, which, as shown, is a
can combustor that is positioned between the compressor 106 and the
turbine 110.
FIG. 2 illustrates a view of an axial compressor 106 that may be
used in gas turbine engine 100. As shown, the compressor 106 may
include a plurality of stages. Each stage may include a row of
compressor rotor blades 120 followed by a row of compressor stator
blades 122. Thus, a first stage may include a row of compressor
rotor blades 120, which rotate about a central shaft, followed by a
row of compressor stator blades 122, which remain stationary during
operation. The compressor stator blades 122 generally are
circumferentially spaced one from the other and fixed about the
axis of rotation. The compressor rotor blades 120 are
circumferentially spaced about the axis of the rotor and rotate
about the shaft during operation. As one of ordinary skill in the
art will appreciate, the compressor rotor blades 120 are configured
such that, when spun about the shaft, they impart kinetic energy to
the air or working fluid flowing through the compressor 106. As one
of ordinary skill in the art will appreciate, the compressor 106
may have many other stages beyond the stages that are illustrated
in FIG. 2. Each additional stage may include a plurality of
circumferential spaced compressor rotor blades 120 followed by a
plurality of circumferentially spaced compressor stator blades
122.
FIG. 3 illustrates a partial view of an exemplary turbine section
or turbine 110 that may be used in a gas turbine engine 100. The
turbine 110 may include a plurality of stages. Three exemplary
stages are illustrated, but more or less stages may be present in
the turbine 110. A first stage includes a plurality of turbine
buckets or turbine rotor blades 126, which rotate about the shaft
during operation, and a plurality of nozzles or turbine stator
blades 128, which remain stationary during operation. The turbine
stator blades 128 generally are circumferentially spaced one from
the other and fixed about the axis of rotation. The turbine rotor
blades 126 may be mounted on a turbine wheel (not shown) for
rotation about the shaft (not shown). A second stage of the turbine
110 is also illustrated. The second stage similarly includes a
plurality of circumferentially spaced turbine stator blades 128
followed by a plurality of circumferentially spaced turbine rotor
blades 126, which are also mounted on a turbine wheel for rotation.
A third stage also is illustrated, and similarly includes a
plurality of circumferentially spaced turbine stator blades 128 and
turbine rotor blades 126. It will be appreciated that the turbine
stator blades 128 and turbine rotor blades 126 lie in the hot gas
path of the turbine 110. The direction of flow of the hot gases
through the hot gas path is indicated by the arrow. As one of
ordinary skill in the art will appreciate, the turbine 110 may have
many other stages beyond the stages that are illustrated in FIG. 3.
Each additional stage may include a plurality of circumferential
spaced turbine stator blades 128 followed by a plurality of
circumferentially spaced turbine rotor blades 126.
A gas turbine engine of the nature described above may operate as
follows. The rotation of compressor rotor blades 120 within the
axial compressor 106 compresses a flow of air. In the combustor
112, as described in more detail below, energy is released when the
compressed air is mixed with a fuel and ignited. The resulting flow
of hot gases from the combustor 112 then may be directed over the
turbine rotor blades 126, which may induce the rotation of the
turbine rotor blades 126 about the shaft, thus transforming the
energy of the hot flow of gases into the mechanical energy of the
rotating shaft. The mechanical energy of the shaft may then be used
to drive the rotation of the compressor rotor blades 120, such that
the necessary supply of compressed air is produced, and also, for
example, a generator to produce electricity.
Before proceeding further, it will be appreciated that in order to
communicate clearly the present invention, it will become necessary
to select terminology that refers to and describes certain parts or
machine components of a turbine engine and related systems,
particularly, the combustor system. Whenever possible, industry
terminology will be used and employed in a manner consistent with
its accepted meaning. However, it is meant that any such
terminology be given a broad meaning and not narrowly construed
such that the meaning intended herein and the scope of the appended
claims is unreasonably restricted. Those of ordinary skill in the
art will appreciate that often a particular component may be
referred to using several different terms. In addition, what may be
described herein as a single part may include and be referenced in
another context as consisting of several component parts, or, what
may be described herein as including multiple component parts may
be fashioned into and, in some cases, referred to as a single part.
As such, in understanding the scope of the invention described
herein, attention should not only be paid to the terminology and
description provided, but also to the structure, configuration,
function, and/or usage of the component, as provided herein.
In addition, several descriptive terms may be used regularly
herein, and it may be helpful to define these terms at this point.
These terms and their definition given their usage herein is as
follows. The term "rotor blade", without further specificity, is a
reference to the rotating blades of either the compressor or the
turbine, which include both compressor rotor blades and turbine
rotor blades. The term "stator blade", without further specificity,
is a reference the stationary blades of either the compressor or
the turbine, which include both compressor stator blades and
turbine stator blades. The term "blades" will be used herein to
refer to either type of blade. Thus, without further specificity,
the term "blades" is inclusive to all type of turbine engine
blades, including compressor rotor blades, compressor stator
blades, turbine rotor blades, and turbine stator blades. Further,
as used herein, "downstream" and "upstream" are terms that indicate
a direction relative to the flow of a fluid, such as the working
fluid through the turbine. As such, the term "downstream" refers to
a direction that generally corresponds to the direction of the flow
of working fluid, and the term "upstream" generally refers to the
direction that is opposite of the direction of flow of working
fluid. The terms "forward" or "leading" and "aft" or "trailing"
generally refer to relative position in relation to the forward end
and aft end of the turbine engine (i.e., the compressor is the
forward end of the engine and the end having the turbine is the aft
end). At times, which will be clear given the description, the
terms "leading" and "trailing" may refer to the direction of
rotation for rotating parts. When this is the case, the "leading
edge" of a rotating part is the edge that leads in the rotation and
the "trailing edge" is the edge that trails.
The term "radial" refers to movement or position perpendicular to
an axis. It is often required to described parts that are at
differing radial positions with regard to an axis. In this case, if
a first component resides closer to the axis than a second
component, it may be stated herein that the first component is
"radially inward" or "inboard" of the second component. If, on the
other hand, the first component resides further from the axis than
the second component, it may be stated herein that the first
component is "radially outward" or "outboard" of the second
component. The term "axial" refers to movement or position parallel
to an axis. Finally, the terms "circumferential" or "angular
position" refers to movement or position around an axis.
FIGS. 4 and 5 illustrates an exemplary combustor 130 that may be
used in a gas turbine engine and in which embodiments of the
present invention may be used. As one of ordinary skill in the art
will appreciate, the combustor 130 may include a headend 134, which
generally includes the various manifolds that supply the necessary
air and fuel to the combustor, and an end cover 136. A plurality of
fuel lines 137 may extend through the end cover 136 to fuel nozzles
or fuel injectors 138 that are positioned at the aft end of a
forward case or cap assembly 140. It will be appreciated that the
cap assembly 140 generally is cylindrical in shape and fixed at a
forward end to the end cover 136.
In general, the fuel injectors 138 bring together a mixture of fuel
and air for combustion. The fuel, for example, may be natural gas
and the air may be compressed air (the flow of which is indicated
in FIG. 4 by the several arrows) supplied from the compressor. As
one of ordinary skill in the art will appreciate, downstream of the
fuel injectors 138 is a combustion chamber 141 in which the
combustion occurs. The combustion chamber 141 is generally defined
by a liner 146, which is enclosed within a flow sleeve 144. Between
the flow sleeve 144 and the liner 146 an annulus is formed. From
the liner 146, a transition piece 148 transitions the flow from the
circular cross section of the liner to an annular cross section as
it travels downstream to the turbine section (not shown in FIG. 4).
A transition piece impingement sleeve 150 (hereinafter "impingement
sleeve 150") may enclose the transition piece 148, also creating an
annulus between the impingement sleeve 150 and the transition piece
148. At the downstream end of the transition piece 148, a
transition piece aft frame 152 may direct the flow of the working
fluid toward the airfoils that are positioned in the first stage of
the turbine 110. It will be appreciated that the flow sleeve 144
and the impingement sleeve 150 typically have impingement apertures
(not shown in FIG. 4) formed therethrough which allow an impinged
flow of compressed air from the compressor 106 to enter the
cavities formed between the flow sleeve 144 and the liner 146 and
between the impingement sleeve 150 and the transition piece 148.
The flow of compressed air through the impingement apertures
convectively cools the exterior surfaces of the liner 146 and the
transition piece 148.
Referring now to FIG. 6, a system for monitoring material defects
according to an exemplary embodiment of the present invention is
provided. This exemplary embodiment is described in relation to
usage within the transition piece 148 of the combustion system. As
provided below, however, it will be appreciated that is description
is exemplary only and that the present invention may be used with
other ducts through which combustion gases or hot gases flow,
including the liner 146. According to the present invention, the
interior surface of the transition piece 148 may be coated with an
insulator coating 161. In some embodiments, the insulator coating
161 may comprise a thermal barrier coating. In particular, a
zirconia oxide thermal barrier coating may be used in certain
preferred environments. However, the present invention is not
limited to this type of coating. Any coating that, relatively
speaking, provides electrical insulation may be used. That is, any
coating that is suitable for use in the turbine environment and
proves to be less electrically conductive as the underlying
structure of the transition piece 148 or combustion duct may be
used. It will be appreciated that the insulator coating may also
have an electrical conductivity that is less than the combustion
gases that, during engine operation, flow through the transition
piece 148. In some embodiments, the insulator coating may consist
of ceramic materials, corrosion coatings, or combustion
products.
As shown, a first electrode 163 may be electrically connected to
the transition piece 148. It will be appreciated that the
transition piece 148 may be metallic and have a high electrical
conductivity. A second electrode 164 may be positioned such that it
is electrically exposed to the hot-gas path (and not connected to
the transition piece 148). One manner in which this may be done is
to have the second electrode 164 pass through the transition piece
148 but be electrically insulated from the transition piece 148 by
an electrically insulating material or structure 165, while also
having a conducting tip 166 that is exposed to the hot-gas path, as
shown in FIG. 6. As such, the second electrode 164 may be
positioned, at least in part, such that it is exposed to the
hot-gas flow path and in proximity to the first electrode 163. In
an exemplary embodiment, the second electrode 164 may be positioned
downstream of the first electrode 163 and/or downstream (or toward
the downstream end) of the transition piece 148. The second
electrode 164 may be constructed of materials capable of
withstanding the rigors of the hot-gas flow path. For example, the
conducting tip 166 of the second electrode 164 may be made of
copper, silver, manganese, silicon or other suitable materials.
The first electrode 163 and the second electrode 164, as indicated
in FIG. 6, may be connected to a control unit 170. The control unit
170 may include a voltage source that is configured to apply a
voltage across the two electrodes 163, 164. The voltage source may
include any conventional systems or equipment having a power or
voltage supply. The control unit 170 also may include an amp meter
or similar instrument for determining or detecting if current flows
between the two electrodes 163, 164 and/or measuring the level of
current flowing between the two electrodes 163, 164.
During normal operation, it will be appreciated that there will be
no or relatively little current detected by the control unit 170 as
flowing between the two electrodes 163, 164. This is due to
electrical insulation of the insulator coating 161 that covers the
inside surface of the transition piece 148. That is, the insulator
coating 161 may separate the voltage being applied to the
transition piece 148 from the hot gases of the flowpath. However,
when a crack originates at any location along the interior of the
transition piece 148, it will be appreciated that it may undermine
the insulator coating 161 and eventually cause a defect 173, as
indicated in FIG. 6. More specifically, the crack may eventually
cause spallation of the thermal barrier coating (or other insulator
coating) such that an exposed patch or portion or area of the more
electrically conductive surface of the transition piece 148 is
exposed to the hot gases of the flowpath during engine
operation.
It will be appreciated by those of ordinary skill in the art that
the combustion gases of the hot-gas flowpath are relatively
electrically conducting and that an electric circuit 180 may form
when the surface of the transition piece 148 is exposed. That is,
the hot gases may conduct electricity between the exposed surface
of the transition piece 148 (which has become exposed because of
the erosion or spallation caused by a defect 173 within the
transition piece 148) and the conducting tip 166 of the second
electrode 164. As such, the control unit 170 will detect that
current is flowing between the two electrodes 163, 164 and that the
electric circuit 180 has formed. In exemplary embodiments, the
detection of the circuit 180 may cause the system to provide a
warning notification that a defect 173 is likely and/or that
corrective action should be taken. The sensitivity of the system
may be adjusted by using different voltages or requiring certain
current thresholds be satisfied before a warning notification is
issued.
In an alternative embodiment, a current may be observed as flowing
between the two electrodes 163, 164 during normal operation, which
becomes elevated when a defect 173 occurs. This may be due to the
fact that certain types of protective insulator coatings are
electrically conductive (or, at least, more electrically conductive
than other types of coatings). Accordingly, in this case, during
normal operation, it will be appreciated that there will be a level
of current observed by the control unit 170 between the two
electrodes 163, 164. However, when a crack originates that
undermines the insulator coating causing spallation of the coating
or simple erosion of the insulator coating causes a portion of the
more electrically conductive surface of the transition piece 148 to
become exposed to the combustion gases of the hot-gas flow path, an
increased level of current flowing between the two electrodes 163,
164 will be observed by the control unit 170. In this embodiment,
the observation of the increase in current provides the warning
signal for a defect 138. As before, the detection of the increased
current through circuit 180 may cause the system to provide a
warning notification that a defect 173 is likely and/or that
corrective action should be taken. The sensitivity of the system
may be adjusted by using different voltages or requiring certain
current thresholds or, in the case of this embodiment, thresholds
indicating a certain level of current change be satisfied before a
warning notification is issued.
In some embodiments, the conductivity of the hot gases of the flow
path may be increased by doping the fuel with a conductive material
or injecting a conductive media in to the flowpath of compressed
air within the compressor of the engine. It will be appreciated
that the injection of a conductive material may enhance the level
of current flowing between the electrodes and increase the accuracy
of the detection system. In some embodiments, the injection of a
conductive doping material may be done periodically during test
cycles in which tests for defects (i.e., crack formation or coating
spallation) are performed. As stated, this temporary measure may
increase the accuracy of detection of defects. In addition, the
size of the defect 173 may be determined by calibrating the system
with the magnitude of current flow through the formed electrical
circuit 180 given the voltage applied and prior defect sizes as
well as other relevant conditions (i.e., whether a doping agent is
present, etc.). For example, higher current levels will be
indicative of bigger defect sizes. Threshold current levels may be
set that indicate defects of certain sizes.
In the absence of a crack forming along the interior surface of the
transition piece, simple erosion or spallation of the electrical
insulting coating 161 also may cause a defect 173 that exposes the
metallic surface of the transition piece 148 to the hot gases of
the flow path. That is, spallation or erosion of the thermal
barrier coating regularly occurs without the formation of a
transition piece crack. Whatever the case, the exposed surface that
results will cause the formation of the electrical circuit 180
between the two electrodes 163, 164 and, thereby, cause the
detection of a current by the control unit 170 that indicates such
a defect is present. The spallation may be caused by the wearing
away or erosion of the insulator coating 161 within the transition
piece 148. In this case, the system may prevent the deterioration
of the exposed material and/or subsequent the formation of cracks
or more serious defect by providing a warning of the defect 173. It
will be appreciated that, absent corrective action, spallation may
result in increased thermal strain to interior surface of the
transition piece 148 and/or material deterioration, which may cause
catastrophic system failures without corrective action.
Testing has confirmed the function of the present invention. For
example, in one test, two electrodes were positioned within the
transition piece of a combustor in a manner consistent with the
description above. A voltage source was connected to the electrodes
and approximately 5V was applied across them. A threshold current
(i.e., the indicator current) of approximately 1.25 microamps was
set. The test results showed that, given these parameters, the
detectable spallation size (i.e., the area of transition piece
surface exposed to the hot gases) was approximately 0.5
inches-squared. That is, the test results showed that a defect that
resulted in exposing at least 0.5 inches-squared of the inner
surface of the transition piece caused the threshold or indicator
current to be exceeded. The parameters, of course, may be adjusted
depending on the characteristics of the system and the desired
sensitivity, as one of ordinary skill in the art will
appreciate.
It will be appreciated by one of ordinary skill in the art that the
above application is exemplary and that these same methods of
detecting defects in other ducts through which combustion gases are
directed. For example, the same methods as described above in
relation to the transition piece 148 may be applied in similar
fashion to the liner 146 of the combustion system, or, for that
matter, in other similar ducts. As such, when reference is made
within the appended claims to a "combustion duct", it will be
appreciated that this includes both the transition piece 148 and
the liner 146. Also, as stated, such a reference may include any
other similar duct through which combustion gases flow.
It will be appreciated that by monitoring crack formation and
coating spallation while the engine operates may reduce the need
for regular visual inspections, which may also reduce engine down
time. As will be appreciated, typically the transition piece 148
and the liner 146 are not inspected until the combustion system
undergoes a diagnostic check after several thousands of hours of
operation. Monitoring for crack formation and spallation while the
engine operates may detect the formation of a significant defect
that otherwise would have gone unnoticed until this inspection
occurs. Depending on the severity of the defect, significant damage
may occur if the engine continues to operate and corrective action
is not taken, particularly if a failure liberates pieces of the
transition piece or liner or other such duct that cause damage to
downstream components. Such an event may be avoided if the
real-time monitoring capabilities of the present invention are
available.
As one of ordinary skill in the art will appreciate, the many
varying features and configurations described above in relation to
the several exemplary embodiments may be further selectively
applied to form the other possible embodiments of the present
invention. For the sake of brevity and taking into account the
abilities of one of ordinary skill in the art, all of the possible
iterations is not provided or discussed in detail, though all
combinations and possible embodiments embraced by the several
claims below or otherwise are intended to be part of the instant
application. In addition, from the above description of several
exemplary embodiments of the invention, those skilled in the art
will perceive improvements, changes and modifications. Such
improvements, changes and modifications within the skill of the art
are also intended to be covered by the appended claims. Further, it
should be apparent that the foregoing relates only to the described
embodiments of the present application and that numerous changes
and modifications may be made herein without departing from the
spirit and scope of the application as defined by the following
claims and the equivalents thereof.
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